During a semiconductor device manufacturing process, various types of gas processing such as film formation processing and etching are executed on a substrate, which may be a semiconductor wafer (hereafter simply referred to as a “wafer”). During such processing, a specific film present on the wafer may be selectively removed through etching by using a resist film formed on the surface of the substrate as a mask and the resist film may then be removed through ashing. A substrate processing apparatus that executes an ashing process normally includes a stage with a built-in heater disposed inside a processing chamber thereof and ashes the wafer on the stage by supplying an electrical current to the heater to heat the wafer to a high temperature of, for instance, 400° C. or higher.
The heater built into the stage may be, for instance, an infrared heater that heats the wafer placed on the stage with radiant heat (infrared rays). As the wafer is heated with the heater, the heat originating from the heater is directly conducted to members constituting the heater, raising the temperature of the stage as well. Thus, if the stage is installed directly at the bottom of the processing chamber, the heat at the stage is conducted to the bottom of the processing chamber, giving rise to a concern that components disposed at the bottom with a lower level of heat resistance (e.g., an O-ring, a sensor and an electrical wiring) may be adversely affected. In order to inhibit heat transfer as the heat is conducted from the stage to the bottom of the processing chamber, a cooling mechanism for cooling the bottom area inside the processing chamber may be installed as disclosed in patent reference literature 1 listed below. However, the installation of such a cooling mechanism in the processing chamber will complicate the structure and the manufacturing cost will also increase. In other words, it is more desirable to address the issue by maintaining structural simplicity without installing a cooling mechanism or the like.
For instance, a stage 30 may be set away from a bottom area 10 of the processing chamber, as shown in FIG. 8, by installing an upright support 20, constituted of a material having a low coefficient of thermal conductivity, which ranges upright from the bottom 10 of the processing chamber and supports the stage 30. However, while the components may be protected from the heat from stage 30 simply by supporting the stage 30 on the upright support 20, they may still be adversely affected by infrared rays (radiant heat) originating from the heater. Namely, since the infrared rays (radiant heat) from the heater are radiated towards the bottom 10 of the processing chamber present below the stage, as well as the substrate set above the heater, the bottom area 10 of the processing chamber, too, may become heated.
The extent to which the bottom area 10 of the processing chamber becomes heated with radiant heat may be minimized by installing an upright support 20 so as to set apart the stage from the bottom 10 of the processing chamber over a greater distance. However, the use of such a long upright support will necessitate an increase in the size of the processing chamber and this is not desirable. In addition, since the intensity of the infrared rays from the heater rises as a higher target temperature is selected for the substrate, the height of the upright support, too, will have to be correspondingly increased and an increase in the size of the processing chamber becomes necessary.
Since it is definitely undesirable to increase the size of the processing chamber, the length of the upright support 20 may be minimized by, for instance, installing a heat shield plate 40 between the stage 30 and the bottom 10 of the processing chamber so as to block the infrared rays from the heater at the heat shield plate 40 and thus reduce the quantity of infrared rays reaching the bottom 10 of the processing chamber.
However, the structure in which the stage is supported on the upright support imposes certain restrictions with regard to the installation of the heat shield plate, i.e., the heat shield plate must be installed so as not to interfere with the upright support, e.g., by installing the heat shield plate so as to surround the upright support. In the example presented in FIG. 9, an insertion hole 42 is formed in the heat shield plate 40 and the upright support 20 is inserted through the insertion hole 42. In this case, a gap is formed between the upright support 20 and the insertion hole 42 at the heat shield plate 40. The infrared rays originating from the heater may be transmitted through even a small gap formed between the upright support and the insertion hole to reach the bottom area 10 of the processing chamber. It is to be noted that a similar phenomenon will occur when a power supply electrode is connected to the lower side of the heater, with a reflector installed further downward relative to the heater, as in the case of the stage disclosed in patent reference literature 2 listed below. Namely, a gap is formed between the electrode and the hole formed at the reflector through which the electrode is inserted and the infrared rays from the heater may thus be transmitted through the gap to reach the bottom of the processing chamber and heat the bottom area unnecessarily in the processing chamber equipped with a stage disclosed in patent reference literature 2 listed below.
Furthermore, the stage upright support in the substrate processing apparatus in which the wafer is heated to a high temperature as described above is often constituted with a material having a high level of heat resistance, e.g., quartz. However, a highly heat resistant material such as quartz itself tends to readily transmit infrared rays. For this reason, even if the reflector is installed without forming any gap between the reflector and the upright support constituted of quartz or the like, the infrared rays from the heater will be transmitted through the upright support itself to reach the bottom of the processing chamber and the bottom area of the processing chamber will be heated unnecessarily.    Patent reference literature 1: Japanese Laid Open Patent Publication No. 2003-059788    Patent reference literature 2: Japanese Laid Open Patent Publication No. 2005-166830